Modbus, Profibus, DeviceNet, CANOpen and Ethernet-based networks are utilized in factory automation and related fields for communicating between data processing systems and peripheral devices. Local area networks (LAN) interconnect factory equipment and other devices such as programmable logic controllers (PLC), fieldbus couplers (FBC), industrial power monitors, e.g., any of the Quantum PLCs by Schneider Automation Inc., and computer work stations for monitoring and programming PLCs and other devices related to factory automation. The Modbus protocol is widely used for factory automation applications. The Modbus protocol is described in the “Modbus Protocol Reference Guide,” publication PI-MBUS-00 by Schneider Automation Inc. and is incorporated herein by reference. Modbus Plus is a LAN protocol for industrial control applications. Applications of the Modbus Plus protocol are described in the “MODBUS Plus Network and Installation Guide,” 890 USE 100 00 Version 3.0, Schneider Electric, April. 1996, and is incorporated by reference.
The Modbus protocol is well known and is described, for example, on the World Wide Web, (Web) at modicon.com/techpubs/toc7.html, and is incorporated herein by reference along with all related Web pages. Different networking schemes relating to factory automation are described in U.S. Pat. Nos. 6,151,625; 5,805,442; 5,251,302; and 5,699,350, and are also incorporated herein by reference.
A Modbus frame comprises three basic parts. The first part is an address field for storing a device identifier (ID). The ID identifies the slave device to which the Modbus frame is to be sent when the message is being sent from a master device. When the frame originates at a slave device and is to be sent to a master device, the ID identifies the slave device from which the Modbus frame was sent. Thus, a master addresses a slave by placing the slave address in the address field of the message, and when the slave sends its response, the slave places its own address in the address field to inform the master which slave is responding. Further contained in the Modbus frame is a function code. The function code informs the receiving device what type of function or operation will be performed by the Modbus frame. For example, a function code, “126,” causes a subsystem of devices to start or stop depending upon function code “126's” sub-function code, i.e., 1 or 2. Yet another function code, function code “125,” reads the hardware identification to the master device. The last part of the Modbus frame includes a data field containing data pertinent to the function code in question, i.e., a CANOpen message for function code “43” in the present invention
The type of CANOpen message determines the means of communication between the nodes on the CANOpen network. CANOpen is a standard and is described, for example, on the Web at can-cia.de.html, and is incorporated herein by reference along with the related web pages. A typical CANOpen network allows communication among and between many operably connected devices from different manufacturers.
To communicate process data from the node-device, a Process Data Object (PDO) message is used. To communicate configuration data from and between node-devices, a Service Data Object (SDO) is used to update the node's Object Dictionary (OD). The OD contains a list of devices and what each device controls, e.g., temperature, pressure, etc. Each node is connected to one or more input/output devices that measure and control a process. Different control systems are described in U.S. Pat. Nos. 6,151,640; 6,122,686; 6,111,886; 5,978,578; 5,598,149; 5,754,548; and 5,557,545. Thus, a Modbus device on a CANOpen network must be able to read and write CANOpen messages to communicate with other CANOpen devices on the network.
Although Modbus has become an industry standard, other technologies have been developed for different automation activities. Modbus is a serial communication protocol that has a limited number of nodes in a master/slave relationship. The master node is the network node issuing the Modbus frame, while the slave node is the receiver of the Modbus frame. In addition, Modbus is limited to 256 bytes in length.
As the industry moves toward interoperability, that is, a seamless data transfer between data transfer protocols such as CANOpen, the number of third party devices requiring addressing increases, further increasing maintenance and complexity of network addressing schemes. CANOpen is a third party protocol that has brought enhanced performance and openness, but not without its limitations.
This invention is directed to solving these and other problems.